Drift boundary approximations in simple magnetospheric convection models

Abstract

We analyze features of particle behavior in magnetospheric convection using simple analytic forms for the electrostatic potential which have been used in other recent works. We show that analytic approximations for the shape and position of surfaces delimiting closed and open particle orbits can be derived. These approximations are good for any pitch angle and at most energies. They break down only for the medium‐energy protons that are predicted by such models to penetrate far inside the plasmapause. The expressions we derive allow rapid tests of a variety of electric field models when analyzing particle data, and we illustrate this by intercomparing field models with several observations.

Electrodynamics of the inner magnetosphere observed in the dusk sector by CRRES and DMSP during the magnetic storm of June 4–6, 1991

“…This boundary separates equipotentials that contact the magnetopause from those that circulate within the plasmasphere. The empirical fitting index 9' describes the degree of penetration to the inner magnetosphere, 9'-i corresponds to full penetration and 9' = oo to full shielding [Southwood and Kaye, 1979 [VoHand, 1975;Stern, 1975]. Elements of the VollandStern model relevant to this study are described in an appendix.…”

The inner edge of the plasma sheet and the diffuse aurora

“…A second theoretical approach is based on calculations of the motion of individual particles in a dipole magnetic field and a model electric field (Kavanagh et al, 1968;Kivelson and Southwood, 1975;Southwood and Kivelson, 1975;Ashour-Abdalla, 1975, 1976;Ejiri, 1978;Southwood and Kaye, 1979). Particle diffusion is not considered, at least initially.…”

Study of Characteristics of Polar Cap Auroras in DMSP Images.

“…The physical basis for a strong rotation of the symmetry axis into the afternoon sector for KP 2 is not yet understood. and Kaye (1979), and Hughes et al (1979). Kaye (1980) suggested that the tendency toward lower values of y with increasing K. reflects a more dynamic mangetosphere in which shielding layers do not have sufficient time to become fully developed.…”

“…In the equatorial plane of the magnetosphere the potential from which the total electric field is derived is assumed to be of the form: (1978) it is easily shown that the equation for the boundary is: Southwood and Kaye (1979) have shown that an excellent approximation to the solution of (4) is axis of symmetry into the evening sector at times of low Kp is due to ionospheric charge pile up near the day-night terminator (Wolf, 1970).…”

“…The statistical sample z was large enough to show that for the same value of B z I further equatorward shifts occur 1) if a substorm is in progress, 2) during the summer, and 3) with increasing magnetic local time. A comparison of the low-latitude boundary of the oval projected into the magnetic equatorial plane with the shape of calculated zero-energy Alfvdn layers (Kivelson, 1976;Southwood and Kaye, 1979) met with mixed success. For the remainder of this paper we refer to the work of Sheehan and Carovillano (1978) and Kamide and Winningham (1977) as S-C and K-W, respectively.…”